The disclosure relates generally to gas turbines, and more specifically, to a pneumatically-actuated bypass valve for selectively controlling bypass air flow in a combustor of a gas turbine.
Gas turbines typically include a compressor, a combustor section including one or more combustors, and at least one turbine section. Compressor discharge air is channeled into each combustor where fuel is injected via a plurality of fuel nozzles, mixed with air, and burned. The combustion gases are then channeled through a transition duct to the turbine section, which extracts energy from the combustion gases.
Gas turbine combustion systems typically operate over a wide range of flow, pressure, temperature, and fuel/air ratio operating conditions. Controlling combustor performance is required to achieve and maintain satisfactory overall gas turbine system operation and to maintain acceptable emissions levels (e.g., NOx and CO levels).
Extended turndown is highly desirable in today's power market where renewable energy sources are increasingly prevalent. These renewable energy sources are changing the operating profile for conventional power plants, driving more cyclic operation. With greater turndown, it is more economical to keep a gas turbine running at very low power during low periods of power demand, and available to add power to the grid as soon as the power output of renewable energy sources decreases (e.g., due to changes in input of wind or solar energy over the course of a day).
During load reductions, or “turndowns,” it is important that combustion systems remain in emissions compliance. In order to maintain acceptable fuel-to-air ratios at the required turndown levels and to control the formation of NOx and CO, it is sometimes desirable to cause a portion of the compressor discharge air from the compressor section to bypass the reaction zone of the combustors. The bypass air is generally reintroduced into the duct of a combustor downstream of the reaction zone.